Polarity, HCN Lewis Structure, Molecular Geometry, Hybridization, and MO Diagram

Hydrogen Cyanide is a very hazardous acid that is notorious for irritating the eyes and respiratory system when inhaled in large quantities.

The material is available in liquid or gaseous form and is colourless.

HCN has a very strong and unpleasant odour that is offensive to people. The odour can be described as almonds that are bitter.

It is considered a dangerous and poisonous material that must be stored with care to prevent any leaks or combustion, as containers exposed to excessive heat may explode.

HCN has a molecular weight of 27,025 g/mol.

The compound has a melting point of 7.9 degrees and a boiling point of 78.1 degrees Fahrenheit.

The following reactions or processes result in the formation of this compound:

When methane interacts with ammonia and oxygen, hydrogen cyanide and water are produced. This reaction is completed by the use of platinum as a catalyst.

2 CH4 + 2NH3 + 3O2 ——-> 2HCN + 6H2O

There are further techniques for producing HCN, but they require an external force or energy, such as reactor walls, to produce this chemical.

Did you know that HCN is also found in nature? There are various sources from which we can acquire HCN.

HCN may be extracted from fruit pits.

Some researchers have stated that HCN can be found in neurons.

Inhaling HCN is quite hazardous. The chemical is disseminated so rapidly within our bodies that its effects are immediate. The molecule can be digested by the human body if it is inhaled in modest quantities. Crazy enough, wouldn’t you say?

Now that we’ve covered the fundamentals, let’s examine the Lewis structure of the chemical and determine how the bonds in HCN are generated.

HCN Lewis Structure

HCN is one of the chemicals with a very unusual and distinct Lewis structure. For a comprehensive knowledge of the Lewis structure, let’s proceed step by step through the notion.

As a refresher, Lewis’s structure is a graphical representation of the many bonds and lone pairs of electrons between two or more atoms in a molecule.

Finding the valence electrons is the first stage in the creation of a Lewis structure.

Here, we must locate the valence electrons of the hydrogen, carbon, and nitrogen atoms.

Hydrogen has only one valence electron because it is an exception to the octet rule and hence does not require eight electrons to fill its octet but only one.

Similarly, Carbon has four valence electrons and Nitrogen has five.

The atomic number of carbon is six, therefore two electrons are in the’s’ orbital and four are in the outer orbital; thus, the number of valence electrons in carbon is four.

The atomic number of Nitrogen is seven, therefore after two electrons occupy the’s’ orbital, the remaining five occupy outer orbitals, resulting in a valence electron count of five.

Now, in order to calculate the total amount of valence electrons, we will add the valence electrons of all three atoms:

=1+4+5 = 10 valence electrons.

The next step is to depict the Lewis dot structure of the compound. See the illustration below:

Carbon is the core atom in this compound because it is the least electronegative element and hence the most stable.

Hydrogen is the least electronegative element, yet it cannot be a central atom because it only has one free electron.

The remaining two atoms, H and N, share a single bond with C.

To make the picture clear, we must also depict the remaining pair of lone electrons on the atoms after the formation of the initial bonds.

After sharing two electrons with hydrogen and nitrogen, carbon retains two additional electrons in its outer shell.

Hydrogen’s octet is full, hence it contains no lone pairs.

After sharing an electron with carbon, nitrogen is left with four electrons, which translates to two lone pairs of electrons.

Balance the charges on the compound in the third step.

Therefore, an abundance of lone pairs will render the molecule unstable in nature. Thus, more bonding will occur between carbon and nitrogen.

As a result, carbon can form two additional bonds with nitrogen, leaving nitrogen with only one pair of unpaired electrons.

This is the most stable Lewis structure for HCN possible.

We hope you have a clear understanding of how HCN bonds are formed. Now, let’s examine the compound’s hybridization.

Combination of HCN

The interbreeding of HCN and sp.

Finding the hybridization of any chemical is crucial since it reveals how the electrons are dispersed among different orbitals.

There is a straightforward formula for determining the hybridization of HCN.

= GA + [VE – V – C]/2


GA = group of atoms bound to a central atom

VE = valence electrons on the atomic nucleus

V equals the valency of the core atom

C = any charge carried by a molecule

Here, GA is 2, VE is 4, Valency of Carbon is 4, and the molecule possesses no charge.

Now, by incorporating these variables into the formula,

= 2 + [4 – 4 – 0]/2

= 2

The hybridization is hence sp.

HCN Molecular Geometry

Why determine HCN’s molecular geometry?

Having observed the Lewis structure of HCN, we must now examine the 3D depiction of the chemical.

And to determine this, we must determine the compound’s molecular geometry. With the aid of the VSEPR theory, determining the molecular geometry of any chemical is simplest.

According to the VSEPR diagram given below, if the atoms of this compound are placed in the general formula, the shape of HCN is linear.

This is due to the fact that A refers to the centre atom and X refers to the other nearby atoms, which are 2 in the case of HCN, resulting in the formula AX2.

HCN MO (Molecular Orbital) Diagram

What exactly is a MO Diagram?

The MO diagram is just a depiction of how the chemical bonds in any compound are generated. The figure depicts various energy levels and the reasons why a molecule occurs in nature or why other compounds do not exist at all.

We can learn more about a compound’s internal structures, bond sharing, and varied orbital energies with the use of this theory.

Consider how the atomic orbitals of HCN combine to form the molecular orbitals.

C has an electronic configuration of 2s2 2p2, H has an electronic configuration of 1s1, and N has an electronic configuration of 2s2 2p3.

Here, one sp orbital of C and one 1s orbital of H fuse.

And the other sp orbital of Carbon fuses with one of Nitrogen’s p orbitals. C and N’s px orbitals create sigma bonds, whilst their Py and Pz orbitals produce perpendicular Pi bonds.

Orientation of HCN

Let us now determine whether the chemical is polar or nonpolar. Let’s determine the electronegativity of each atom here first.

The electronegativity of carbon is 2.55, the electronegativity of hydrogen is 2.2, and the electronegativity of nitrogen is 3.04.

As can be seen, there is not a large difference between the electronegativity of carbon and nitrogen, yet despite this, the results are significant.

Nitrogen in this combination will attempt to attract the electrons of Carbon. As a result, the nitrogen atom will have a negative charge, rendering this combination slightly polar.

Additionally, you must include HCN polarity.

Consequently, we might say that this molecule is polar.

As there are now repulsions within the atoms, it is easy to conclude that there is also a bond angle between the atoms. This compound has a linear form, and the bond angle can be recognised as 180 degrees.


This was a chemical that was highly interesting to research. Here, the characteristics and bond formation are quite remarkable.

Now, let’s briefly review what we’ve learnt thus far.

HCN is an extremely poisonous chemical with a smell reminiscent of bitter almonds.

There is one bond between hydrogen and carbon, but three between carbon and nitrogen. There is a solitary pair of

electrons on the atom of nitrogen.

The substance exhibits sp hybridization.

The atomic structure of HCN is linear.

The substance is polar by nature.

We hope you have an understanding of this compound’s Lewis structure, hybridization, and molecular geometry.

If you have any queries or concerns, you can contact us.

We appreciate your reading!

Read more: MO Diagram, CN Lewis Structure, Molecular Geometry, Hybridization, and Polarity

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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